I'm in the middle of polishing my parents silver A4 cabriolet and although it's in fantastic condition there are a couple of light scratches. I have some AG Paint Renovator but try as I might it doesn't seem to do anything at all. Has anybody had any good results with this stuff and if so what did you do to achieve them?

I've used my da with a variety of polishes. I bought the AG stuff a while back and haven't really used it until now. AG advise to not use it with a machine. On another note; it's my first time doing a metallic silver car and I certainly haven't got the same sense of achievement from this colour. It looks pretty much the same as it did before only cleaner. You can't beat the dark colours for car cleaning.

I've tried different polishes on various panels. I've used menzerna 400 through to 3800, some britemax one step stuff, srp, ultra deep shine and Blackfire GEP. I used a medium pad with all of it and a soft black pad with some of it. Good results and I got a few light marks out of the paint. When I first used the britemax A10 (green stuff) I wrote it off as a waste of time. However used properly over with patience it gives great results. The car was washed with farecla stripping shampoo then clayed using Blackfire shampoo as a lube, washed again then polished. It's all topped off with some obsession evolution. I didn't like that at first, either but now I really like using it. Great beading and really easy on/off.

Silver and white clean and polish in exactly the same way as black, red and blue, the difference is that the defects (or lack thereof) are much harder to see on lighter paint. One reason is that when we see scratches and swirls etc on dark paint its not the actual damage that we see but the edge of it, the edge or side of a scratch is always white, so it stands out like a sore thumb against the dark background, which you don't get on light paint, the edges of the damage blend in more.

The other reason is to do with the way different colours reflect light, someone did explain it to me once and it was all very scientific and to do with refraction rates and spectrum absorbtion and stuff, but I didn't understand a word so its pointless me trying to explain it. Suffice to say, because light is actually made up of all different colours lighter coloured paintwork reflects a broader spectrum of the visible light whereas darker colours absorb more of it, which in non-geekoid means we see it different and you know, just cus and stuff.

Basically the only solution is to use specific directional lighting, a high powered led torch works well, even better when it is the only light source, all of which means working inside where you can control the lighting. If that is not possible and you are at the mercy of the big light bulb in the sky then you have to make do, sun glasses help and I've heard that polarised lenses are even better, but not tried them. If you have the choice, work in shade or when it is overcast, if not then chances are you won't be able to see fully what you are (or aren't) doing.

This is a perfect example, with the camera exaggerating the effect that we see with the human eye, the areas of the car in sunlight just look silver and blank, but only the part in shade shows the gloss and reflection.

Autoglym says to use it by hand and not machine, so by that I take it that it needs to be aggressively rubbed in to work if it going to! Don't know what machine you have but I'm assuming a DA? If it's not a big throw or direct drive you may be bogging down, therefore you can sit there all day and not achieve anything. Or scratches are deeper than thought, then you'll never move them!